Magnesium salts of coal acid coatings



Oct. 30, 1962 H. B. RICKERT 3,051,466

MAGNESIUM SALTS 0F COAL ACID COATINGS Filed Aug. 16, 1957 v I N VEN TOR. A/erber/ 5. Kicker) 0 TTORNE Y5 United States Patent 3,061,466 MAGNESIUM SALTS 0F COAL ACID COATINGS Herbert B. Rickert, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Aug. 16, 1957, Ser. No. 678,622 3 Claims. (Cl. 117124) This invention has reference to the magnesium salts of the polycarboxylic acids which may be derived from the oxidation of coal (hereinafter referred to as coal acids) and to the water-plastified protective films and coatings, as Well as various coated articles, that may advantageously be obtained therewith. The chief aim and concern of the present contribution to the art is to provide the indicated varieties of novel and utile compositions and various desirable articles and structures obtainable therewith.

Amongst the many known chemical commodities that r are in existence are the so-called coal acids, from and with which the essential compositions of the present invention are derived and prepared. Such polycarboxylic acids as are contemplated herein may be identical with or similar to those which may be obtained by the oxidation with gaseous oxygen, which may be contained in air, of an aqueous alkaline slurry of a finely divided carbonaceous material selected from the group consisting of coal and coke that has been obtained by the carbonization of coal at temperatures beneath about 700 C. Coal acids that have been obtained by the nitric acid oxidation of suitable carbonaceous materials are also generally satisfactory. Such coals that are of the varieties known as anthracite, bituminous, sub-bituminous and lignite and other low grade coals are generally suitable for the manufacture of coal acids. Satisfactory cokes are those produced according to conventional techniques from coal at a temperature beneath about 700 C. The utilization of higher coking temperatures frequently causes the cokes that are obtained to be graphitic and rendered unsuitable for conversion to coal acids in satisfactory yields.

The free coal acids product is a hygroscopic, usually yellowish, essentially water soluble material. It is believed to be substantially comprised of various aromatic polycarboxylic acids. The average molecular Weight of the coal acids that are ordinarily obtained is frequently in the neighborhood of 2502'70, or so, generally being greater than 200 but not in excess of 300. Their average equivalent weight, generally about 80, is usually greater than 70 but seldom exceeds 90. The free coal acids ordinarily appear to have an average of from two and one-half to five carboxylic groups per molecule with an apparent average of three to four being common. While their exact chemical nature and constitution may be somewhat conjectural, they evidently contain considerable quantities of triand tetra-carboxylic benzene acids as well as aromatic acids having more complex nuclei. Frequently, for example, the greatly preponderant proportion of aromatic nuclei obtained in coal acids prepared in the described fashion have been found to consist of methylnaphthalene, benzene, biphenyl, naphthalene, phenanthrene, alkyl benzene, benzophenone and toluene nuclei.

The magnesium salts of coal acids of the present invention are water soluble materials that, in the dry state, are a powdery amorphous solid having a yellow to brown coloration. Frequently, for example, the magnesium salts are obtained as a yellowish-orange powder that has an apparent bulk density in the neighborhood of 0.836 gram per cubic centimeter. Despite the fact that the barium and calcium salts of coal acids, for example, are only partially insoluble in water, the magnesium salts of the present invention dissolve readily and completely in water with solubility characteristics that are at least comquantity of application.

mensurate to those of the alkali metal (including ammonium) salts of the free coal acids. The magnesium salts are miscible with water in all proportions, as evidenced by the fact that evaporation of water from an aqueous solution of the magnesium salts does not cause them to precipitate when greater concentrations are attained. The apparent viscosity of aqueous solutions of the magnesium salts of coal acids, surprisingly enough, is appreciably greater than the viscosity of an aqueous solution of the free coal acids at equivalent dissolved concentrations. This phenomenon is believed to be due to the capability of the magnesium salts of the present invention to enter into intermolecular associations to form polymer-like structures. The magnesium salts of coal acids are generally insoluble in most of the common organic solvents such as methanol, acetone, benzene, carbon tetrachloride, ethyl acetate, petroleum ether, and the like.

The magnesium salts of coal acids are hygroscopic in nature and will absorb moisture from the atmosphere; the precise amount in particular instances depending upon the relative humidity of the air (or other gaseous atmospheric medium) in which they are exposed. They have excellent film-forming properties when they are plastified with water and, in such condition, are well adapted to provide smooth, hard, tightly-adhering films or protective coatings over various substrates to which they may be applied such as glass, various metals (including steel and other ferrous alloys) plastics such as polystyrene and the like, wood and so forth. The amount of physically combined water that is necessary to plastify the magnesium salts of coal acids to develop their optimum film-forming properties varies with equilibrium conditions of the salt in the atmospheres at various relative humidities in which they are exposed. In this connection, contrary to the behavior that is experienced with water plastified films of the free coal acids, the films according to the present invention of the magnesium salts retain their essential and desirable characteristics and do not become pronouncedly tacky, even under conditions of relative humidity that are as high as or more percent.

Film coatings of the magnesium salts of coal acids may be provided readily by simply applying an aqueous solution of the salt over the desired substrate and evaporating it until the salt film forms. As has been indicated, the moisture content of the resulting film is generally in equilibrium with the atmosphere. Any desired applicating technique may be utilized. The evaporation may conveniently be permitted to occur under the influence of normal room temperatures. Or, if so desired, heat may be applied for the purpose. It is generally convenient to employ film-forming applicating solutions of the salts that have a dissolved solids content between about 2 and 60 percent by weight, based on the weight of the solutions. As is apparent, more concentrated solutions of the salts require less evaporation for film formation when such an application is intended. The film that is obtained may literally have any desired thickness, depending upon the manner and the Films having thicknesses of from about one to five mils, for example, are not at all difiicult to achieve.

Films of the magnesium salts of coal acids are sometimes more attractive to apply over certain substrates than are films of the free coal acids. This is because of the tendency of the latter materials to chemically attack or corrode various materials. This is particularly the case when a completely or substantially completely neutralized magnesium salt is utilized for the coating application, which species of the salts, incidentally, is preferred in the practice of the invention. Typical of the substrates which may sometimes be adversely or undersirably affected by contact with free coal acids films are steel of the common variety (such as mild carbon alloys) and certain cellulosic materials such as fibers, yarn, and cloth and fabric constructed therefrom of cotton or viscose rayon (and other regenerated or reconstituted cellulosic textiles) or both. With reference to the latter varieties of textile substrates, it is particularly advantageous to employ water plastified films of coal acids upon yarns and threads thereof as a warp size or the like finish thereon during their weaving or other construction into cloth and fabric. The magnesium salts of the present invention have excellent and most advantageous utility in such application.

Thus, an aqueous solution of from 2 to percent by weight or so, of the magnesium salts may be applied as a warp size to viscose rayon filament yarn by conventional slashing means and techniques in order to provide a finish application of the water plastified film on the yarn of from about 5 to percent by weight, based on the weight of the applied film under equilibrium conditions and taken on the dry weight of the yarn, or more or less as may best be suited to meet the requirements of particular situations.

A most convenient manner of preparing the salts of the present invention is to neutralize an aqueous solution of the free coal acids with magnesium hydroxide. As has been indicated, it is preferable for the magnesium salts product to be completely or substantially neutralized. The salts can be recovered by evaporation of the resulting solution thereof to dryness. Or, if they are intended to be employed for film-forming purposes as an applicating solution, a neutralized reaction mass which contains the salts can be prepared at (or evaporated or diluted to) a suitable and desired concentration for direct application thereof.

The invention is more particularly illustrated in and by the following examples wherein, unless otherwise explained, all percentages are to be taken by weight.

EXAMPLE A About 7.3 grams of magnesium hydroxide, Mg(OH) was slowly added to about 41.5 grams of a 50 percent aqueous solution of free coal acids having a molecular weight of about 270 and an equivalent weight of about 83. During the addition the mixture became hot. After all the magnesium hydroxide had been added, the mixture was cooled to about 60 C. and filtered in order to remove a minor proportion of silica that had been introduced with the magnesium hydroxide.

The resulting clear solution was deposited by being cast as a film on a glass plate. Upon evaporation of the excess water at room temperature, a clear, smooth, hard and tightly-adhering coating was obtained, having an average thickness of less than five mils. When similar films on glass were conditioned in controlled humidity chambers at both 51 and 76 percent relative humidity at 25 C., the films retained about the same excellent characteristics. In contrast, similar films of the free coal acids were noticeably tacky under such conditions. When steel is coated with a similar water-plastified film of the magnesium salts of coal acids, an excellent protective coating is obtained that prevents the surface of the metal from becoming rusted and corroded during extended periods of exposure to atmospheres of normal humidity in the vicinity of Midland, Michigan. Such hard plastic surfaces as molded polystyrene may also be benefited by application of a similar coating.

EXAMPLE B Following the general procedure of Example A and using free coal acids similar to those therein employed, several formulations comprising varying concentrations in water of magnesium salts of coal acids were prepared by adding different relative quantities of powdered magnesium hydroxide to a 50 percent aqueous solution of the free coal acids. The composition of each of the formulations is indicated in the following tabulation, wherein the quantities of the magnesium hydroxide and the coal acids solution employed for each is indicated, as well as the degree of neutralization achieved in each formulation. Formulation VI, incidentally, contained no magnesium salts since it was the unneutralized coal acids solution which was included for purposes of comparison.

Table 1.Various Magnesium Salts of Coal Acids Formulations Weight in Degree of gms. of 50 Neutraliza- Formulatlon Weight in percent tion of M G gms. of Mg coal acids salts,

(OH): solution percent 7. 3 41. 5 100 11. 6 83. 0 8O 4. 4 41. 5 G0 2. 92 41. 5 2. 92 83.0 20 None 41. 5 0

Table 2.-Properties and Characteristics of Magnesium Salt Films at Room Temperateur Under Difierent Conditions (Percentages) 0 Relative Humidity (RH) Film from Percent Film Film clarity Physical characteristics of film Dryncss-tack free of film formulation RH adhesion I 76 Soft skin on film To finger and foil,

51 Hard, fine cracks Do. 20 Hard, edges starting to powder D0.

0 Fine orange-red colored powder Powder blows 01f plate. II 76 Soft skin on film, tacky underneath.-- To finger and foil.

51 Hard, fine cracks Do. 20 Hard, edges powdered Do, 0 Fine powder Do, III 76 Soft skin on film, tacky underneath.-. Do. 51 Hard, fine cracks Do, 20 Hard, very few cracks. D0. 0 Do. IV 76 Do. 51 Do. 20 Do. 0 Do. V 76 Not; dry.

51 Soft, no cracks-.-" To finger and foil. 20 Hard, smooth, no cracks. D0. 0 Very hard, cracks, edges powdered Do. VI 76 Not homogenous Tacky, almost dry Not dry,

51 Not homogenous, Soft 'lofingerandfoil.

cloudy. 20 Clear Hard, smooth, no cracks Do, 0 do Very hard, few cracks Do.

EXAMPLE C About 500 milliters of a 50 percent aqueous solution of free coal acids similar to those employed in the foregoing were mixed with about 105 grams (3.60 equivalents) of magnesium hydroxide. The starting solution of coal acids that was used a specific gravity of about 1.20 and contained about 3.62 equivalents of the free coal acids. The resulting magnesium salts solution that was prepared had a pH of about 4.70, a specific gravity of about 1.21, and a Gardner viscosity of A. Good films could be made from the solution.

EXAMPLE D Into about 1785 grams of distilled water there was mixed about 350 grams (12.0 equivalents) of powdered magnesium hydroxide. To the resulting mixture there was added about 1992 grams of a 50 percent aqueous solution of free coal acids containing about 12.0 equivalents of the mixed, aromatic, polycarboxylic acids. A 30 percent solids solution of dissolved magnesium salts was thereby obtained. The magnesium salts was thereby obtained. The magnesium salt solution had a pH of about 4.7, a Gardner color number of 17 and a Gardner viscosity of A-3. The resulting solution had good filmforming properties.

EXAMPLE F About 500 milliliters of the coal acids solution used in Example C was mixed with about 106 grams (3.62 equivalents) of magnesium hydroxide. The resulting aqueous solution of magnesium salts of coal acids had a pH of 4.7, a Gardner color number of 18 and a Gardner viscosity of A-2-3. It had good characteristics as a film-forming, coating solution.

EXAMPLE G A stock 50 percent solids content solution in water of magnesium salts of coal acids was. prepared by mixing about 830 grams of a 50 percent aqueous solution (containing 5.0 equivalents) of coal acids with 146 grams (5.0 equivalents) of powdered magnesium hydroxide and additional grams of water. The stock magnesium salt solution (Formulation VII) had a pH of about 4.7 and a Brookfield viscosity in centipoises at room temperature of about 157. Portions of Formulation VII were then diluted with varying quantities of distilled Water to obtain different formulations containing less dissolved solids. The Brookfield viscosity of each of the resulting formulations Was then determined for purposes of comparison with Formulation VII. The results are included in the following Table 3.

Table 3.--Br00kfield Viscosities in Centipoises at Room Temperature of Various Aqueous Solutions of Magnesium Salts of Coal Acids In addition to the dilutions, a fifth portion (Formulation XII) of the stock solution was concentrated by evaporation to a 55 percent solids content. The specific gravity and Brookfield viscosity at room temperature of Formulation XII were 1.275 and 1320 centipoises, respectively. Further concentration of Formulation XII to a greater solids content formulation (62.5 percentFormulation XIII) provided an aqueous solution having a specific gravity of about 1.31 and a Brookfield viscosity of about 49,400 centipoises at room temperature.

In contrast with the foregoing, the Brookfield viscosity at 23 C. of a 48 percent aqueous solution of the same free coal acids from which the above magnesium salts were derived was found to be only about 25 centipoises.

EXAMPLE H Warp ends of filament, 300 denier, viscose rayon continuous filament yarn twisted to about 3 turns per inch were sized by slashing them at room temperature with various aqueous solutions of completely neutralized magnesium salts of coal acids that were prepared in general accordance with the foregoing description to deposit water-plastified sizing films 0n the several yarn samples that had been slashed. The sizing films were formed after the applied solutions were permitted to dry and become conditioned at normal atmospheric conditions. The results obtained are set forth in the following tabulation which includes the number of times (or cycles) each yarn sample that was sized could be flexed on a Duplan cohesion tester before reaching the fray point of the yarn. The fray point tests was performed in the conventional manner following the equipment manufacturers recommendations. Sample Y-l, incidentally, was an unsized control.

Table 4.-Warp Sizes Finishes of Water-Plastified Magnesium Salts of Coal Acids on Viscose Rayon Filament Yam Percent of Percent Tenacity Elongation magnesium pickup on of yarn, yarn, Fray" Yarn salts in yarn (based grams per percent point, sample aqueous on dry denier (Avg. 5 cycles sizing weight of breaks) solution yarn) Excellent performance and results could be obtained when each of the sized yarns were woven into various fabrics. The magnesium salt sizes had no harmful effect on the yarn and could be easily washed oil. of the fabric products by conventional scouring after the fabric construction had been completed. Similar excellent results may be obtained in the warp sizing of spun viscose rayon and cotton yarns and with yarn from the variety of cellulosic artificial silk or rayon that is obtainable by the cuprammonium process if care is taken to adjust the amount of film applied to the particular type of yarn being sized, taking into account the fabric construction to be made with the size product.

In the hereto annexed drawing there is schematically portrayed one of the yarns sized in accordance with the present invention.

The scope and purview of the present invention, including the multitudinous variations possible within its embrace, are to be judged and gauged from the hereto appended claims rather than strictly from the foregoing didactic description and specification.

What is claimed is:

1. A composite article of manufacture comprising a glass substrate coated with a water-plasti fied film of magnesium salts of coal acids, said coal acids being the poly-.

carboxylic acids that are derived from oxidation of coal and the like carbonaceous materials and which typically consists of various aromatic nuclei having an average of from about 2.5 to 5 canboxylic groups per molecule with an apparent equivalent weight of from about 70 to and an average molecular weight between about 200 and 300.

2. A composite article of manufacture comprising a metal substrate coated with a water-plastified film of magnesium salts of coal acids, said coal acids being the polycarboxylic acids that are derived from oxidation of coal and the like carbonaceous materials and which typically 7 consist of various aromatic nuclei having an average of from about 2.5 to 5 carboxylic groups per molecule with an apparent equivalent weight of from about 70 to 90 and an average molecular weight between about 200: and 300.

3. Method for sizing cellulosic yarn and the like which comprises slashing said yarn with an aqueous solution of the magnesium salts of coal acids, said coal acids being the polycar-boxylic acids that are derived from oxidation of coal and the like carbonaceous materials and which coal acids typically consist of various aromatic nuclei having an average of from about 2.5 to 5 carboxylic groups per molecule with an apparent equivalent weight of from about 70 to 90 and an average molecular weight between about 200 and 300, in order to deposit by means of said slashing up to about 25 percent by weight of a water-plastified film of said salts on said yarn, based on the Weight of the yarn, as a finish thereon.

References Cited in the file of this patent UNITED STATES PATENTS 1,637,510 Aileman Aug. 2, 1927 1,829,877 Schroeder Nov. 3, 1931 2,695,910 Asseff et al Nov. 30, 1954 2,699,428 Lux et a1 Jan. 11, 1955 2,762,840 Howard Sept. 11, 1956 2,777,874 Asself et a1 Jan. 15, 1957 2,785,198 Grosskinsky et al. Mar. 12, 1957 10 2,826,515 Rickert et a1 Mar. 11, 1958 OTHER REFERENCES Kinney et al.: Industrial and Engineering Chemistry, vol. 48, No. 2, February 1956, pages 327-332.

Boreham et al.: Journal of Applied Chemistry (London), August 6, 1956, pages 329-333. 

1. A COMPOSITE ARTICLE OF MANUFACTURE COMPRISING A GLASS SUBSTRATE COATED WITH A WATER-PLASTIFIED FILM OF MAGNESIUM SALTS OF COAL ACIDS, SAID COAL ACIDS BEING THE POLYCARBOXYLIC ACIDS THAT ARE DERIVED FROM OXIDATIN OF COAL AND THE LIKE CARBONACEOUS MATERIAL AND WHICH TYPICALLY CONSISTS OF VARIOUS AROMATIC NUCLEI HAVING AN AVERAGE OF FROM ABOUT 2.5 TO 5 CARBOXYLIC GROUPS PER MOLECULE WITH AN APPARENT EQUIVALENT WEIGHT OF FROM ABOUT 70 TO 90 AND AN AVERAGE MOLECULAR WEIGHT BETWEEN ABOUT 200 AND
 300. 